Thermostat assembly

ABSTRACT

A programmable thermostat features a memory unit receptive of unit values of temperature desired at different times on different days all individually or in various combinations both as to days and times. An output device signals a temperature control system. As controlled by a clock, the memory unit is addressed during different times of the different days to provide a signal representing the corresponding value desired. Existing temperature level is sensed and compared with each value so as to develop an error signal. In response to that error signal, the output is operated in a direction to reduce the difference between actual and desired temperatures. Numerous details as to layout, construction and circuitry are presented.

The present invention relates to a thermostat assembly. Moreparticularly, it pertains to a variety of system, circuitry andmechanical aspects of a unit for governing the program of temperaturecontrol within a building or other space.

As confirmed by many studies, substantial savings in energy usage may beobtained through appropriate adjustment of heating and cooling units togovern their operation in accordance with actual requirements. It hasbeen demonstrated that the mere act of reducing a household thermostatlevel during sleeping hours can result in worthwhile savings in the costand use of energy. Analogously, there may be other times during thetotal day in which adjustment of thermostat control advantageously couldbe modified in order to accommodate such things as level of activity,presence within the space concerned and the like.

It has long been known to associate a thermostat with a clock-actuateddevice which automatically turns down the temperature level soughtduring normal sleeping hours. Such devices typically are programmableonly to the extent of allowing a manually fixed change of temperaturethat is applied to every day of the week.

It also is known, nevertheless, to program a giventemperature-determining system by varying the energization of thecontrolling unit in accordance with selected time schedules. Inaddition, it has been recognized that electronic components areavailable for the purpose of replacing the mechanical clocks formerlyassociated with such controls and also to provide an illuminated displayof the temperature conditions under observation and control.

Notwithstanding the aforementioned general recognition of the desire tobe able to control temperature conditions within a space and theprovision of time-controlled devices for automatically dictating changesin operation, that which has heretofore been suggested seems to havesuffered from a lack of flexibility in its manner of control,substantial cost of implementation, and either complete dependence uponexisting power sources or the need for a cumbersome auxiliary powersource.

With the advent of the microcomputer contained within a very smallpackage, it has become apparent that the control and operation of manydifferent appliances and the like may be enhanced, both as to flexiblityof control and efficiency, by incorporating the techniques associatedtherewith. Joined with other solid-state components for controllingsignificant amounts of power, the microcomputer has "opened the door" toan almost unlimited variety of improvements in various devices thatpreviously were operated by means of mechanically-operated switchessometimes associated with such familiar apparatus as relays andsolenoids for the purpose of ultimately handling the higher power levelsinvolves with different machines and appliances.

It is a general object of the present invention to take advantage of theaforedescribed development of the art in order to provide a new andimproved thermostat.

Another object of the present invention is to provide new and improvedimplementations of electronics circuitry advantageously usable inachieving the general objective.

A further object of the present invention is to provide a new andimproved approach to thermostat control.

Still another object of the present invention is to provide a new andimproved mechanical assembly for a thermostat and its systems.

In accordance with one aspect of the invention, a programmablethermostat includes a memory unit together with means for entering intothat memory unit values of temperature desired at different times ondifferent days of a week all individually and in various combinations ofdays and times involved. An output device controls one or both ofheating and cooling systems. All operation is governed by a clock. Undercontrol of the clock, the memory unit is addressed during the differenttimes of the different days so as to provide a signal representative ofthe unit value for temperature. At the same time, existing temperatureis sensed. That value signal is compared with the existing temperaturelevel so as to develop an error signal. In response to the error, theoutput device is operated in an appropriate manner to reduce themagnitude of the difference between actual and desired temperatures. Theinvention also includes numerous details of improved circuitry and ofhousing for enclosing the circuitry and making the entire thermostatdesirable for implementation and usage.

The features of the present invention which are believed to bepatentable are set forth with particularity in the appended claims. Theorganization and manner of operation of the invention, together withfurther objects and advantages thereof, may best be understood byreference to the following description taken in connection with theaccompanying drawings, in the several figures of which like referencenumerals and/or letters identify like elements, and in which:

FIG. 1 is a block diagram of a system embodying the present invention;

FIGS. 2-5 when taken together constitute a schematic diagram ofcircuitry for implementing the approach depicted in FIG. 1;

FIG. 4A is a schematic representation of a subcomponent included withina component shown in FIG. 4;

FIG. 4B is a schematic diagram of an alternative for a portion of thecircuitry shown in FIG. 4;

FIG. 5A is a schematic diagram of a circuit included within a componentshown in FIG. 5;

FIGS, 6, 7 and 8 depict waveforms of various signals appearing withinthe circuitry;

FIG. 9 is an isometric view of a programmable thermostat of theinvention and contained within a housing certain underlying componentsbeing visible through a transparent cover;

FIG. 10 is a top plan view of the thermostat shown in FIG. 9;

FIG. 11 is a bottom plan view thereof;

FIG. 12 is a front elevational view thereof;

FIG. 13 is a side elevational view thereof;

FIG. 14 is an exploded isometric view thereof, a battery cover shown inFIGS. 9 and 10 having been removed;

FIG. 15 is a top plan view of a mounting plate shown in FIG. 11 asaffixed to the rear of the housing, two spring contacts and a switchlever having been removed;

FIG. 15A is a fragmentary side-elevational view taken along the line15A--15A in FIG. 15;

FIG. 16 is a bottom plan view of a base portion of the housing;

FIG. 16A is a cross-sectional view taken along the line 16A--16A in FIG.16 and rolled over by 180°;

FIG. 17 is a top plan view of a case portion of the housing, certainassociated components, shown in FIGS. 9, 10 and 14, having been removed;

FIG. 17A is a view taken along the line 17A--17A in FIG. 17;

FIG. 18 is a bottom plan view of the case, again with certain componentsremoved;

FIG. 19 is, from left to right, a top plan view, a bottom plan view anda side elevational view of a contact shown in place in FIG. 15;

FIG. 20 is, from left to right, a side elevational view and a rearelevational view of a component shown in FIG. 14 as assembled;

FIG. 21 is a bottom plan view of a cover shown in FIG. 14;

FIG. 21A is an enlarged cross-sectional view taken along the line21A--21A in FIG. 14;

FIG. 22A is an enlarged fragmentary isometric view of a component shownin FIG. 14 as connected to a component shown in FIG. 25;

FIG. 22B is an enlarged side elevational view of a subcomponent shown inFIGS. 14 and 22A;

FIG. 23A is, from left to right, an end elevational view and a top planview of a component represented in FIG. 5 and indicated in FIG. 14;

FIG. 23B is an enlarged side elevational view of another sub-componentshown in FIG. 14 as mounted in a fragmentary segment of a substratethereof;

FIG. 23C is an isometric view of a mounting rack which, in a modifiedembodiment, may be used in conjuction with the components of FIGS. 23Aand 23B;

FIG. 24 is, from right to left, a side elevational view and a top planview of a cover plate assembled in place in FIG. 10 but there overlaidby a decal shown in FIG. 26;

FIG. 25 is a top plan view of a component the major portion of which isshown in FIGS. 9, 10 and 14 and another portion of which is shown inFIG. 22A, there also being one modification shown in FIG. 25 as comparedwith those earlier figures; and

FIG. 26 is an enlarged plan view of a decal shown in FIGS. 1, 10 and 14and mentioned above in connection with FIG. 24;

In the foregoing description of the figures, the terms "top" and"bottom" have reference to the thermostat in the orientation of FIG. 9as, for example, sitting on a table. In use most of the time, the"bottom" of the thermostat usually will be face-to-face with a verticalwall.

FIG. 1 depicts an overall system. It includes power supply and switchingcircuitry 100, a battery monitor 102, a timer 104, a microcomputer andclock 106, a temperature sensor 108, a keyboard 110 and a display 112.As indicated, unit 100 has power, control or other connection to theremaining components of the system. In general, all of the illustrated"blocks" interact with each other. A detailed implementation of thesystem of FIG. 1 is depicted in FIGS. 2-5.

As specifically embodied in FIGS. 2-5, it is assumed that there is to beadaptation to a conventional heating and/or cooling apparatus whichinvolves a twenty-four volt control system for operational purposes.That is, primary operating power for the particular embodiment disclosedherein is intended to be derived from an existing heating or coolingunit as normally would be available at the site desired for athermostat. In addition, there would be present at that site wiringintended to energize a solenoid or the like which controlled operationof a furnace and there also may be wiring which would similarly energizean air cooler and, often separately, its fan or blower. In theconventional twenty-four volt control system for many heating andcooling units, the controlled solenoid is connected directly in serieswith the secondary winding of a step-down transformer. Consequently,only two wires between the controlled unit and the thermostat arenecessary to permit both energization of the solenoid, by switchingcontained in the thermostat, and the supply of power from thetransformer to the thermostat. While the specific embodiment isparticularly configured to permit direct connection to that type ofconventional system, its interfacing circuitry may readily be modifiedto accommodate other control arrangements that require three-wire orfour-wire interconnection between the thermostat and the controlledunit.

In addition, other ultimate applications are available, and they mayrequire modification. For example, the overall system might be adaptedto govern a heat-control system that did not, in itself, providenecessary input power for the herein disclosed apparatus. In that case,of course, a separate transformer would be included between a powersource and this apparatus. Also, the associated heating or coolingapparatus might not be subject to the normal twenty-four volt controlsystem. An example would be now-conventional resistance-heatedspace-warming systems that operate from conventional building suppliesat one-hundred-twenty or two-hundred-forty volts. In such a case, anadaptor unit would be interposed between that which is illustrated andthe supply to the heating elements, typically involving relays orsolenoids for switching higher levels of voltage and/or current.Alternatively, the comparatively low-power solid-state output switcheshereinafter described would be replaced with higher-power devices. Whilenot forgetting those clear alternatives, the description hereinafterwill proceed on the basis of interface with an at least somewhat moreordinary heating or cooling system each of which employs two-wiretwenty-four volt control and supply for primary operation and, perhaps,an added wire for separate blower operation.

Generally with regard to FIGS. 2-5, different individual components havebeen dominated by the use of nomenclature which has become conventionalin the art. Thus, a capacitor is denoted by the letter "C" and aresistor by the letter "R". Additionally, numerous ones of the differentcomponents are incorporated within standard integrated circuits formedon so-called chips each of which includes a number of such components.Labeling has been employed to indicate which of those components are incommon on the same chip. For example, the label IC3 is applied toseveral different components, as will hereinafter be individuallyidentified, to indicate that they all are embodied herein as a portionof the same chip.

Throughout the drawings, various numerals appear adjacent to differentterminals but without lead lines. These always refer to conventionalmanufacturer's designations with regard to the components concerned. Forexample, within each rectangular block that represents acommercially-available component, there is a series of numbers; thoseare the pin numbers assigned as a standard practice with respect to suchcomponents. A lightening-flash symbol is used to indicate opticalcoupling to another component, and those two components will have thesame "IC" designation.

Where a terminal is not otherwise denominated, connection as betweendifferent ones of FIGS. 2-5 may be traced by the use of a letter ornumber in one figure which corresponds with the same letter or numberutilized in a related figure. In addition, various test points areindicated by terminals labeled with the symbol "TP" plus a number. Theseare for use in testing and servicing and will not be further mentioned.

The power supply and switching arrangement 100 is detailed in FIG. 2. Aterminal 120 connects to the available twenty-four volt source providedby the heating system, such as a furnace, to be controlled. A terminal121 supplies a control voltage or signal back to the heating unit forenabling its energization. Typically, the signal from terminal 121energizes a solenoid at the furnace which opens its main fuel supply orotherwise causes the heating unit to activate and develop its desiredheat output.

Bridging terminals 120 and 121 is a TRIAC 123 the gate of which isconnected to the collector of an opto-transistor 124 and the emitter ofan opto-transistor 125. Also bridging terminals 120 and 121 is theseries combination of a resistor R35 and a capacitor C16. In a knownmanner, these serve as a snubber network to prevent misfiring of TRIAC123 by reason of the voltage-current phase relationships. The emitter oftransistor 124 is returned to terminal 121 through a diode D1, and itsbase is connected to its emitter by a resistor R33. The collector oftransistor 125 is returned through a diode D3 to terminal 121, while itsbase is connected back to its emitter by a resistor R34. Diodes D1 andD3 provide protection for transistors 124 and 125 against reverse bias.Also bridging terminals 120 and 121 are the input terminals of a bridgerectifier 126 in series with a resistor R4 that is shunted by acapacitor C10. The negative output terminal of rectifier 126 isconnected to ground, while its positive output terminal is connected toa supply bus 127 that extends to the input terminal of a Darlingtontransistor 128. The output terminal of transistor 128 is connected to aterminal 129 and provides a sub-component supply voltage Vcc.

The input of transistor 128 (also Q3) is shunted by a resistor R16 andthe input base is returned to ground (GND) or Vdd through a zener diodeVR2. The output emitter of transistor 128 is coupled to ground over acapacitor C12. A capacitor C11 is coupled between the input side oftransistor 128 and ground.

A capacitor C3 is coupled from bus 127 to ground through resistors R8and R9 with the series combination of those resistors being shunted by acapacitor C2. Coupled to the junction between capacitor C3 and resistorR8 is one side of an opto-TRIAC 132 the other side of which is returnedto output terminal 121. A pair of resistors R14 and R15 extend in seriesbetween the output of transistor 128 (Vcc) and ground. The junctionbetween resistors R14 and R15 is connected to the plus inputs of each ofcomparators 133 and 134. The minus input of comparator 133 is connectedto the junction between resistors R12 and R13 which form a voltagedivider extending between bus 127 and ground. The minus input ofcomparator 134 is connected to the junction between resistor R8 and R9.

Three different opto-diode 135, 136 and 137 are optically coupled to theinput or gate of respective opto-TRIAC 132 and opto-transistors 124 and125. Diode 136 is connected from the output terminal of comparator 133through resistors R31 and R10 and diodes 135 to ground. Diode 137 isconnected from the output terminal of comparator 134 through a resistorR11 to the junction between resistors R10 and R31. The different Vccleads, such as through terminal 129, are coupled to ground by acapacitor C13 connected physically close to the Vcc terminal ofmicrocomputer 106.

When control of an air conditioner is desired in addition to control ofa furnace or other heating unit, unit 100 includes a module 138 whichpresents output terminals 139, 140 and 141. Terminal 139 supplies powerto run the air conditioner, and terminal 140 separately supplies powerto the fan of that air conditioner. A switch 142 may be closed to bridgeterminals 139 and 140 when operation of the fan is to be automatic andto bridge terminals 140 and 141 to command continuous fan operation.Terminal 141 receives the conventional twenty-four volt controlpotential available from such an air condition or, in the alternative,is connected by a jumper 143 so as to be connected to the twenty-fourvolt input available from the heating unit. Connected between terminals141 and 139 is a TRIAC Q4 the gate of which is returned through anopto-TRIAC 144 to terminal 139. The optical-input gate of TRIAC 144 iscoupled to an opto-diode 144a (FIG. 4).

Operation of the power supply and switching system of FIG. 2 is enabledby a signal which arrives through a terminal 145 that is connected tothe junction between resistors R10 and R31. The system is designed sothat approximately eight-five percent of the available power input istransferred through TRIAC 123 for purposes of energizing the solenoid orother actuator in the furnace. At the same time, the amount ofmonitoring power required by the system is sufficiently low to avoidfalse actuation of the furnace solenoid.

When the system of FIG. 2 is in the "off" mode, rectifier 126 stillchanges the twenty-four volt alternating-current input into directcurrent. In this mode of operation, all of the optically-coupled devicesare disabled. The output direct current from rectifier 126 is storedacross the combination of capacitors C2 and C3. Regulation of the outputvoltage is achieved by means of the series combination of resistor R16and diode VR2. In conjunction with Darlington transistor 128, of course,the output circuit exhibits a high gain, so that a substantial degree ofvoltage stability is obtained. Accordingly, the internal operatingpotential Vcc is available during the "off" mode of operation forenergizing all of the other components and sub-systems.

The "on" mode of operation serves to fire TRIAC 123 and thus deliver thetwenty-four volt alternating-current supply voltage directly on to theheater solenoid or other activator that controls operation of thefurnace or other source of heat. When TRIAC 123 is fired to supply theoutput operating potential to the heating unit, it is still necessarythat power be maintained in the controller as developed by rectifier126. To this end, TRIAC 123 is triggered part way into each half cycleof supplied input power and after charging capacitors C2 and C3.

Comparators 133 and 134 are used to monitor the voltages acrosscapacitors C2 and C3. For effective operation with a regulated outputvoltage Vcc of nine volts, typical operation requires that the voltageon C3 available at the input terminal of transistor 128 should rise toapproximately twenty volts at the beginning of each half wave. Thisallows the current drain of the unit to discharge capacitors C2 and C3during the remainder of each half wave without affecting the regulatedoutput voltage Vcc.

The voltage divider established by resistors R14 and R15 serves tosupply comparators 133 and 134 with a refernce voltage, in the instantsystem of approximately 4.5 volts. The enabled input through terminal145 is in a "high" state when heating is demanded.

The waveform as exhibited across TRIAC 123 is shown in FIG. 6. As thepotential increases on each negative half-wave, current is enabled toflow through TRIAC 132 in order to change capacitor C2, the return beingestablished to the other side of the incoming alternating-current linethrough rectifier 126. The divider established by resistors R8 and R9 isselected so that, when capacitor C2 is charged to ten volts in thisexample, the voltage on the negative input of comparator 134 becomesequal to the reference voltage of 4.5 volts. When capacitor C2 becomesfully charged, during the negative half wave of the input cycle, to justabove ten volts, the output of comparator 134 switches to "low". Thatallows current in the enabling signal through terminal 145 to flowthrough resistor R11 and light-emitting-diode (LED) 137.

As indicated above, diode 137 is an opto-coupler, such as a 4N30, ofwhich transistor 125 is an optically-coupled part. During the negativehalf wave of the incoming power, the "low" side of the effectivealternating-current line is positive with respect to the gate of TRIAC123. Accordingly, when capacitor C2 is charged to just above theten-volt level mentioned, comparator 134 switches its output state.Current then is allowed to flow through diode 137 and the optical outputfrom diode 137 activates transistor 125, so that current flows throughthe latter and diode D3 into the gate of TRIAC 123. That triggers orfires the latter and achieves the ultimate result of connectingterminals 120 and 121. At this point, capacitor C2 discharges to a valuebelow ten volts. That deactivates diode 137 and allows TRIAC 123 toreset to its open state on the next zero crossing of the waveform.

On the positive half wave of each cycle of the input alternating-currentsupplied, current flows through rectifier 126 and begins to chargecapacitor C3. That current flows through opto-TRIAC 132 back to the"low" side of the alternating-current input system. The divider ofresistors R12 and R13 establishes a reference such that, when thevoltage level on bus 127 reaches twenty volts, the output of comparator133 switches to a "low" state. With capacitor C2 charged as describedpreviously, C3 is then charged to a value of ten volts to causecomparator 133 to switch to "low" and draw current through terminal 145by way of resistor R31 and light-emitting diode 136. The opticalemission from the latter is coupled into its associated transistor 124,so as to cause the triggering of TRIAC 123 by allowing current to flowfrom the gate of the latter through transistor 124 and diode D1. Shortlyafter TRIAC 123 is triggered, the output of comparator 133 switches to"high" and, thereby, allows TRIAC 123 to once more reset on the nextzero crossing.

During operation on either half cycle, light-emitting diode 135 istriggered by the signal received over terminal 145, so as to activateits associated TRIAC 132 by means of the optical coupling between thosetwo elements. It will be observed that the system of FIG. 2, includingcapacitors C2 and C3, is actually a voltage-doubling network thatutilizes what amounts to approximately ten volts of the inputalternating-current waveform on each half cycle to achieve a total ofabout twenty volts applied to the regulation system which includes diodeVR2 and transistor 128. Resistors R33 and R34 preferably are includedmerely as noise suppressors so as to prohibit false triggering oftransistors 124 and 125.

Referring again to FIG. 6, it may be seen that a favorable short-terminstability occurs. The first two or three cycles of thealternating-current waveform that occur after the signal receivedthrough terminal 145 goes "high" are entirely shunted across the system.That occurs because the total voltage across the combination ofcapacitors C2 and C3 prior to that "high" signal is equal to the peakvoltage of the alternating-current input which, in the example given, isapproximately thirty-five volts. Therefore, the outputs of comparators133 and 134 remain "low" until capacitors C2 and C3 discharge to thedesired level.

At the heart of the overall temperature control system herein underdescription is a microcomputer 150 as shown in FIG. 4. While itsfunction will be described in more detail hereinafter, it may be notedthat it supplies, from a terminal 2, the signal which, after processingalso yet to be described, provides the enable control signal fed throughterminal 145 to the unit of FIG. 2 that has just been discussed.

For the purpose of operating mode 138 to achieve control of anassociated air conditioning unit, microcomputer 150 also yields anenable output at its pin 3 that is fed in series through a resistor R36and LED 144a which is returned to ground. LED 144a is optically coupledto control the operation as a gate input of TRIAC 144 in module 138.Upon the occurrence of a "high" from microcomputer 150, therefore, TRIAC144 supplies a signal to the gate of TRIAC Q4, so as to apply the basictwenty-four volt control potential from terminal 141 to terminal 139.

LED 144a and resistor R36 are included in a module 138a. With operationusing a REVIEW pushbutton and a permanent program loaded intomicrocomputer 150 as described below, actuation of that pushbuttontemporarily disables LED 144a and, thus, operation of the airconditioner. When that function is not desired, the permanent programmay be changed accordingly, so that LED 144a stays on during the reviewprocedure. Alternatively, the circuit of a module 138a', as shown inFIG. 4B, is substituted for module 138a.

In FIG. 4B, LED 144a is again connected between ground at a terminal 220and one end of resistor R36. The other end of resistor R36 is connectedthrough a diode D15 to receive the output from the output terminal J9'at pin 3 of microcomputer 150. Extending also from that pin 3 is theseries combination of a resistor R40 and a capacitor C17 that returns toground. Connected to the junction between resistor R40 and capacitor C17is one input of a comparator 146 the other input of which is connectedby a terminal 148 to a ground return through a resistor R32 from a pin11 of a display driver 164 described more fully below. The output ofcomparator 146 is connected to the combined inputs of paralleledcomparators 147a and 147b, their combined outputs being connectedthrough a diode D17 to the junction between resistor R36 and diode D15.Those combined outputs also are connected through the series combinationof a diode D16 and a resistor R38 back to the junction between resistorR40 and capacitor C17. Another comparator 149 on the same chip with theothers is disabled by connecting both of its inputs to ground.Energization of the comparators is by way of a connection to terminal216, as indicated, and a ground return.

Also added along with module 138a' is a resistor R26 connected betweenground and an output terminal J5 at pin 26 of microcomputer 150, alongwith a resistor R30 connected between output pins 17 and 22 (Vcc) ofdriver 164. In operation, LED 144a continues to be energized as beforewhen a "high" occurs on output pin 3 of microcomputer 150, and thatsignal also is stored on capacitor C17. When that output goes "low" asdriver 164 is activated, the changed level on terminal 148 enablesenergization of LED 144a through diode D17. The latter condition islatched on by diode D16 which holds the signal on capacitor C17.

It is believed to be desirable that the components of module 138,separately or together with resistor R36 and diode 144a as module 138a(or with module 138a') be physically incorporated into the overallarrangement as at least somewhat separate sub-assemblies. This permitsthe overall system to be manufactured without modules 138 and 138a (or138a') for use in the application of controlling only a heating unit.When the additional control of air conditioning or cooling also isdesired, however, it will be immediately apparent how easily andinexpensively it is to add these other modules so as to employ the sameoverall system to accomplish that additional function of control.

As is now generally known with respect to the implementation ofmicrocomputers such as unit 150, they establish an operating procedurewhich first of all is ordained by their specific design and also isestablished by "loading" or permanent programming at the factory level,so as to exhibit a defined response to ultimate changeable programmingby the user. In terms of information-handling capability, a singlesolid-state microcomputer can perform tasks previously assignedliterally to a roomful of computer apparatus. Perhaps the only drawbackof the present day microcomputer is that its user-supplied variablestorage of input information is subject, by reason of its manner ofapproach, to complete erasure upon loss of supply power to thisfantastic device. Thus, a user program of temperature control enteredinto microcomputer 150 could be lost during a power shortage when thenormal supply potential at terminal 120 was terminated. Also, dependenceupon the supply at terminal 120 would prohibit any kind of remote use ofthe unit herein under discussion.

To overcome the just-mentioned lack of permanent user-programmablestorage in microcomputer 150, the present system includes a battery andmonitoring circuit therefor as shown in FIG. 3. At the outset, thearrangement of FIG. 3 includes a battery 152 in series with areverse-bias-protecting diode D2 and with that series combination beingconnected between ground and the wiring which carries the internalsupply voltage Vcc. Without more, battery 152 serves to insure that theinternal component-supply voltage is maintained regardless of thedevelopment in unit 100 of that same internal supply voltage by way ofrectifier 126. The power available from battery 152 serves to maintainmicrocomputer 150 in its condition of preserving a user-program wheneverthe incoming external supply voltage is interrupted and whetherintentionally or not.

Of course, any battery is subject to deterioration over a period of timeeven if never used. In accommodation, the system in FIG. 3 serves tomonitor the battery voltage and provide a necessary signal tomicrocomputer 150 to indicate the impending failure of the battery. Tothis end, a series of components are distributed so as to extendbasically between a Vcc bus 154 and ground. Thus, a voltage dividercomposed of resistors R5 and R6 extends between bus 154 and ground,resistor R6 being bypassed to ground by a capacitor C6 and resistor R5being bypassed by a diode D14. The junction between resistors R5 and R6is connected to the negative input terminal of a comparator 155. Thatjunction is also connected through a resistor R22 to the collector of atransistor Q6 the emitter of which is returned to ground and the base ofwhich is connected through resistors R21 and R28 back to bus 154.

Another voltage divider, composed of series-connected resistors R2 andR3, is connected from the junction between battery 152 and diode D2 backto ground. In turn, the junction between divider resistors R2 and R3 isconnected to the negative input terminal of a further comparator 156. Atransient suppressor TS1 is shunted across the overall combination ofresistors R2 and R3 for protection from static electricity dischargedinto the battery terminals. Also bridged between bus 154 and ground isthe series combination of a resistor R7 and a zener diode VR1, with thejunction between resistor R7 and zener diode VR1 being connected to thepositive inputs of comparators 155 and 156.

The output terminal of comparator 155 is connected between the junctionbetween resistors R21 and R28 and from there through a diode D9 and aterminal 157 to the initiating (INIT) terminal 9 of microcomputer 150. Acapacitor C14 is shunted between terminal 157 and ground through aterminal 158. Bus 154 is connected through a terminal 159 into the Vcclead. The output terminal of comparator 156 is connected through a diodeD8 and through a terminal 160 to an input terminal K2 of microcomputer150. The output from comparator 156 also is connected through a resistorR29 and a terminal 162 to an output terminal 25 (J4) of microcomputer150 for the purpose of providing a momentary sensing of batterycondition when output terminal 25 is in the "high" state.

In the monitor as shown in FIG. 3, it is comparator 156 which is used todetect the low-battery condition. With the output from terminal 25 ofmicrocomputer 150 set to a "high", a reference level is established onthe output of comparator 156 and against which that comparator mustwork. Battery voltage is divided by resistors R2 and R3 and appears onthe negative input of comparator 156. The relative values of resistorsR2 and R3 are selected such that, if the battery voltage is above apredetermined amount, about seven volts, the voltage at that negativeinput of comparator 156 is above the lower voltage established by diodeVR1, so that the comparator output is maintained in a "low" state. When,however, the battery voltage drops below the predetermined value, thenegative input to comparator 156 falls below the threshold establishedby diode VR1 on the positive input of that comparator. Consequently, theoutput of the comparator then is pulled "high" through R29 connected toterminal 25 of microcomputer 150, and that "high" appears as an input atterminal K2.

Diode D8 serves as a reverse-bias protection against an input fromkeyboard assembly 110 yet to be described. Before discussing keyboard110 and display 112 in detail, it may be noted that, if a logic one isdetected on the input K2 from keyboard assembly 110 to terminal 6 ofmicrocomputer 150, while the signal from terminal 25 of microcomputer150 is high, the program is set up to display a warning to the user thatthe battery should be changed. That warning is visibly indicated ondisplay unit 112 upon depression of either one of START or REVIEWpushbuttons yet to be discussed.

In operation, the "high" signal from terminal 25 of microcomputer 150occurs only about once every four seconds during normal use and for aperiod of time sufficient only to enable the operation of the batterymonitoring function. As indicated in FIGS. 4 and 5, that output fromterminal 25 also is utilized as a drive signal connected at J4 ofdisplay driver 164. Diode D2 serves to prevent the supply voltage fromaffecting the reading by the monitor of battery voltage and alsoprevents charging of the battery.

Comparator 155 continually monitors the supply voltage available tomicrocomputer 150. With a specified minimum supply voltage for theparticular microcomputer employed, the microcomputer may continue to runat a lower voltage but will not necessarily follow the program containedin its read-only memory (ROM). It is, therefore, important thatmicrocomputer 150 be held in a reset mode in case of the existence of abelow-minimum supply voltage. To this end, resistors R5 and R6 dividethe voltage between ground and bus 154 in order to supply the negativepotential to comparator 155. The values of resistors R5 and R6 areselected such that, when the supply voltage equals the specifiedminimum, the potential present on the negative input of comparator 155is slightly less than that established by the voltage regulating actionof zener diode VR1. When, however, the supply voltage is below theestablished minimum limit, the output of comparator 155 is held "high"through resistor R28. That circumstance forces microcomputer 150 to areset mode by way of the connection through diode D9 to terminal 9 ofthe microcomputer 150. At the same time, there is an additionalconnection to ground resistor R5 by way of transistor Q6 which is turnedon when the output of comparator 155 goes "high". The overall effect isto set microcomputer 150 into a reset mode until such time as the supplyvoltage returns to a value sufficiently above the established minimumlevel by about 0.3 volt.

It will be noted that the resetting of microcomputer 150 can only occurat such time as the incoming twenty-four volt alternating-current supplyis lost and operation is being maintained from battery 152.Incidentally, capacitor C6 also is included so as to initiate the resetcondition upon the initial supply of power in energization of theoverall unit. Finally, comparator 155 is depicted as having a directconnection to bus 154, and comparator 156 is shown to have a directconnection to ground. These are the common power supply connections forall of the comparators on a chip IC3.

Turning now to timer 104 as also shown in FIG. 3, it develops a sixtyHertz square wave used by microcomputer 150 in order to keep track oftime. A sample of the input alternating-current waveform as received atterminal 120 (FIG. 2) is conveyed by way of terminal 170 through a zenerdiode VR3 and a capacitor C7 to the input base of a transistor Q5. Thejunction between diode VR3 and capacitor C7 is shunted to ground by wayof the parallel combination of a resistor R41 and a capacitor C8 througha terminal 172.

The collector of transistor Q5 is connected to bus 154 which extends toa power terminal shown on an inverter 174. Analogously, a terminal on aninverter 175 is connected to ground. These are the common power supplyterminals for all of the inverters on a chip IC2. A capacitor C15 shuntsbus 154 to ground.

The emitter output of transistor Q5 is connected to the input terminalof inverter 174 and the output terminal of that inverter is, in turn,fed to the input terminal of inverter 175. The latter has its outputterminal connected through a diode D5 to a terminal 176 which, as willbe seen in FIG. 4, is connected to a microcomputer input pin 5 or K1 towhich a terminal of keyboard 110 also is connected. The output ofinverter 175 is fed back over a capacitor C1 to the input of inverter174, and inverter 174 is bridged by the series combination of a resistorR37 and a potentiometer P1.

Inverters 174 and 175 serve together as associated components of afree-running oscillator that is set to perform at sixty Hertz by meansof adjustment of potentiometer P1. Because temperature variations mayinduce a drift in that pre-set frequency, the free-running mode ofoperation of timer 104 is used only during periods of power loss atterminal 120 (FIG. 2). When supplied alternating-current power isavailable at terminal 120, the operation of timer 104 is synchronized tothe incoming waveform sampled through capacitor C7.

The waveforms present at the cathode of diode VR3 are shown in FIGS. 7and 8. FIG. 7 depicts the waveform whenever the overall heating systemis in the "off" mode. At the time represented by t1, the input voltagehas risen slightly to the value at which diode VR3 begins to conduct.From the time t1 to the time t3, at the peak of the sine wave, thevoltage developed across resistor R41 and capacitor C8 builds up inaccordance with the waveform. The differential of that waveform isconveyed over capacitor C7 to the base of transistor Q5, so as to enableconduction of that transistor and cause charging of capacitor C1 to thesupply voltage. The latter occurrence forces the output of the resultingoscillator circuitry to be synchronized to the incoming line frequency.

When the overall heating system is in its "on" mode, the voltagewaveform presented at the cathode of diode VR3 is generally that shownin FIG. 8. In this manner of operation, conduction of transistor Q5occurs from a time t4 through a time t5. As a result, the oscillationagain is synchronized to the sixty Hertz incoming line frequency. Outputdiode D5 preferably is included in order to prevent destruction ofanother signal that is present on microcomputer input terminal K1 whenthe oscillator output is low.

Being temperature responsive, the overall system, of course, requirestemperature sensor 108. To this end, a temperature-dependent oscillatorarrangement includes series connected inverters 180 and 181. The inputto inverter 180 is enabled through a terminal 182 and a diode D6connected to an output terminal at pin 26 or J5 of microcomputer 150 asshown in FIG. 4. The output of inverter 181 is connected through a diodeD7 and through a terminal 183 back to pin 8 or K8 of microcomputer 150,which pin also is connected to a terminal of keyboard 110 as indicatedin FIG. 5.

The input of inverter 180 is connected to the series combination of aresistor R17 and a capacitor C4 to the output of inverter 181. Thejunction between inverters 180 and 181 is connected to the junctionbetween resistor R17 and capacitor C4 by the series combination of aresistor R18, a potentiometer P2 and a resistor R19. Most importantly,resistor R19 is shunted by a thermistor RT1.

Inverters 180 and 181, together with the associated components,constitute another oscillator. Its frequency is determined by thecombined values of potentiometer P2, resistors R18 and R19 andthermistor RT1 along with capacitor C4. Resistors R18 and R19 serve tolinearize the operation of thermistor RT1 over the desired temperaturerange.

When the output from microcomputer 150 as presented at terminal 26 is"high", sensor 108 is enabled. The number of pulses which end upappearing as an input to terminal 8 of microcomputer 150 (protected bydiode D7) are counted over a full number of sixteen cycles or pulses asreceived by the microcomputer from timer 104. By mathematicalmanipulation in the permanent program, as will be apparent later, thatcount is used to determine the ambient room temperature and to enabledecisions to be made as to enablement or disablement of either theheating or air conditioning systems that are ultimately controlled. Forthe present system, that which has been illustrated may be specified toan accuracy of less than plus or minus one degree Fahrenheit over arange extending between fifty degrees Fahrenheit and eighty-nine degreesFahrenheit.

As shown on the lower portion of FIG. 5, keyboard 110 is composed of afour-by-four matrix of normally-open switches that are pushbuttonoperated. Six of the switch pushbuttons are labeled in that figure withthe terms STORE, START HEAT, START AIR, REVIEW, CLEAR, and AM/PM. Theremaining buttons respectively are marked with the numbers zero throughnine and also, as can be viewed in FIG. 10, have lettering which, aswill be further discussed below, corresponds to different ones of thedays of the week and different combinations of such days.

The matrix includes columns J0, J1, J2 and J3, together with rows K1,K2, K4 and K8. The buttons are distributed so as individually to bridgethe respective different intersections within the array with twoexceptions as shown. That is, both the STORE and the START HEAT buttonsbridge the intersections between the column J0 and row K8, and the STARTAIR button bridges between column J0 and a terminal 190. When thethermostat system is to be incorporated into a model used only for thecontrol of heating, a jumper W1 is connected between terminal 190 androw K8. When, on the other hand, the system is to be used to controlboth heating and air conditioning, jumper W1 is removed and a jumper W2is instead connected between terminal 190 and row K4. In the firstalternative when the system is utilized only for the control of heating,only one of the two START buttons needs to be included. Preferably,however, they are paralleled by being placed side-by-side to form aphysically larger START button.

As will be apparent, columns J0 through J3 are individually connectedthrough respective diodes D10 through D13 to the correspondingly labeledoutput terminals of microcomputer 150 as shown in FIG. 4. Similarly,rows K1, K2, K4 and K8 are connected to the correspondingly labeledinput terminals on microcomputer 150 also as shown in FIG. 4.

The arrangement permits multiplexing of the involved outputs frommicrocomputer 150, while scanning of the inputs K1, K2, K4 and K8 isused to determine which button has been depressed. The arrangementwithin the microcomputer is such that only one of the designated outputsis enabled at any given instant, and only when one of those outputs isenabled are the K inputs scanned. Diodes D10-D13 serve to prevent anysignals on the K input lines from being fed back into display driver164.

Keyboard 110 also preferably includes an overlying conductive shield 192that is connected through a terminal 170 back through the terminal ofthe same number in FIG. 2 so as to be coupled directly to thetwenty-four volt alternating-current supply at terminal 120. However,shield 192 is not exposed to the user. It allows any discharge of staticelectricity to be dissipated harmlessly into the input supplytransformer. Without shield 192, static could discharge through thekeyboard into microcomputer 150, possibly causing permanent damage.

Display 112 includes display driver 164 and a display device 200.Display driver 164 as herein specifically implemented is a DS8872integrated circuit chip as conventionally designated. Its inputterminals as externally designated by the symbols J0 through J8 areconnected to the correspondingly labeled output terminals ofmicrocomputer 150 as shown in FIG. 4. As mentioned above, its pin 11 isreturned to ground through resistor R32 and terminal 220 to the groundpath depicted at the bottom of FIG. 4. Display driver 164 is basically aseries of buffers that also function as inverters in the mannerspecifically illustrated. FIG. 5A depicts the typical circuitry of eachof those buffer-inverters. Thus, each J input terminal of the driver isconnected through a resistor 204 to the base of a transistor 206 thecollector of which leads to a digit cathode in display device 200. Theemitter of transistor 206 is returned to ground, and the base andemitter are shunted by an input resistor 208. Pin 22 of driver 164 isconnected to Vcc through a terminal 129.

As particularly implemented herein, display device 200 is a so-calleddisplay stick of a twelve-digit type, such as that under the commercialdesignation 5082-7445C. Counting from the left in FIG. 5, its fourth andsixth digits are not utilized, and its ninth digit actually is a colonwhile all of the others are conventional seven-segment arrays oflight-emitting diodes, so as to be able to define either numbers orletters in the normal manner. It is intended that the first three digitsfrom the left indicate whether in a heating or air cooling mode andtemperature, such as H72 or A72. The fifth digit indicates the day ofthe week as arbitrarily assigned but later assumed herein to be arepresentation of Sunday as a "1" through the following Saturday as a"7". The remaining digits used present the time, such as "10:30A" forten-thirty in the morning.

The lower line of numbers on device 200 as drawn in FIG. 5 once againare the conventional pin numbers assigned by the manufacturer of thecomponent. Immediately above the row of pin numbers is another row whichsets forth either the segment anode letter or the digit cathode number.As usual, the segment anode letters indicate the terminals which need tobe energized to select display segments within each unit of the display,and the digit cathode numbers refer to which display units within theoverall device are to be energized. Hence, there are no connections tounits four and six which, as indicated, are intended to remain unused.

Accordingly, the seven different terminals assigned to segmentdetermination are labeled "a" through "g" and are connected to receivethat output information from the correspondingly-labeled outputterminals on microcomputer 150 in FIG. 4. For selectively enabling thevarious cathodes, the various pins numbered 12 through 20 in driver 164are individually connected appropriately to display device pin numbers9, 10, 12, 13, 14, 16, 17, 18 and 20, with driver pin 16 also beingconnected to device pin 19. There is no separate connection to the ninthdisplay unit, the colon of that display being illuminated automaticallywhenever the last digit is displaying either an "A" or a "P". Thedecoding for the input lines "a" through "g" is determined withinmicrocomputer 150.

It will be recalled that, in the discussion of the switching system ofFIG. 2, an ultimate command-to-operate or enable signal is derived fromthe sub-system of FIG. 4 and delivered to the sub-system of FIG. 2through a terminal 145. That command signal appears at an output J9(terminal pin 2) of microcomputer 150 as shown in FIG. 4. To achievealmost instant triggering of TRIAC 123, while delaying its return to anon-conductive state for a minimum period following termination of thecommand signal at output terminal J9, the output is connected from thelatter and fed through a network which includes the series combinationof inverters 210 and 211. The latter drives the base of a transistor Q2operated in the emitter-follower mode, so as to provide an ultimatecommand signal from its emitter through terminal 145 to the junctionbetween resistors R10 and R11 in FIG. 2. That same command signal alsois fed through a current limiting resistor R39 and a terminal 214 to thedecimal point segment terminal DP at pin 6 of display device 200. Inoperation, therefore, illumination of the decimal point informs the userthat the thermostat is calling for heat.

The collector of transistor Q2 is returned to internal supply voltageVcc by terminal 129 to which terminal 129' also is connected. Theaforementioned time delay is provided by a capacitor C9 shunted by aresistor R20 and returned from the input of comparator 210 to ground.Increased discharge of capacitor C9 is provided by the seriescombination of a diode D4 and a resistor R1 shunted between the input ofinverter 210 and the output of inverter 211.

Microcomputer 150 is a conventional TMS1100 as commercially designatedand which includes not only the integrated microcomputer circuitry butalso has its own clock. That clock sets the rate at which themicrocomputer executes the permanent program instructions in its readonly memory (ROM). Accommodating the separation of the overall schematicrepresentation, as separated between FIGS. 1 through 5 in accordancewith available space on each sheet of the drawings, the internalpositive operating potential Vcc is made available through a terminal216 from FIG. 2. Analogously, the ground return from pin 4 ofmicrocomputer 150, also labeled Vdd, is shown as connected by a terminal218 to the sub-system of FIG. 2 and also by terminal 220 to thesub-system of FIG. 3. It may be noted that each output of microcomputer150 typically is an emitter-coupled transistor 220a as shown in FIG. 4A.

Setting the frequency of operation of the clock integrated withinmicrocomputer 150 is a network consisting of a capacity C5 coupled onone side to Vcc as at terminal 216 and from its other side through aresistor R27 and a potentiometer P3 to ground. The junction betweencapacitor C5 and resistor R27 is connected to clock-oscillator pinterminals 18 and 19 on microcomputer 150.

Of course, the read only memory in microcomputer 150 must be permanentlyprogrammed or set up to appropriately receive information from andprovide information to the different sub-systems involved and inaccordance with the ultimate nature of the overall functions that are tobe performed. While any two different programmers of the read onlymemory might end up with substantially different schemes for achievingthe same ultimate result, a preferred loading program is fully describedand set forth in FIGS. 27 through 56 of the concurrently filedapplications identified hereinafter and incorporated herein byreference.

After assembly into housing structure yet to be described in more detailand loaded with read only memory programming, the overall thermostat isready for selective programming by the user. Of course, the ordinaryuser would never be able to program the read only memory inmicrocomputer 150 in the manner necessary to achieve the desiredresults. Accordingly, the microcomputer itself and its permanent loadingare selected to allow comparatively simple addressing of the thermostatby the user. Through keyboard 110, the user enters day, time andtemperature information as the basic input data. Certain other functionsalso are available. Those selections are displayed by device 200 and, ifcorrect, the user then is able to store that information, so that itwill govern operation of the thermostat.

To this end, a control panel shown in FIG. 10 includes pushbuttonslabeled essentially as previously described with regard to FIG. 5. Asshown in FIG. 10, however, there is but a single START pushbutton areaand no separate pushbutton with respect to air conditioning. This is thepreferred arrangement when the thermostat is intended for use only inthe control of heating and in the absence of air conditioning. Foreconomy of parts procurement, however, keyboard 110 is in this casefabricated to include a separate pushbutton element for use when airconditioning also is to be controlled. As discussed in more detail inconnection with FIG. 25, all of the actual pushbutton contacts aredisposed beneath a flexible insulative layer on which the labels areprinted. There are, therefore, both START HEAT and START AIR buttoncontacts located side-by-side beneath the single label START on aheat-only model, so that both may be depressed simultaneously.

For such a version intended only to control heating, jumper W1 isconnected and jumper W2 is not connected. At the same time, resistorsR26 and R30 and modules 138 and 138a or 138a' may be omitted. For amodel intended to control both heating and air conditioning, on theother hand, those components are included and jumper W2 is connectedinstead of jumper W1. At the same time, separate START HEAT and STARTAIR labels preferably are used as specifically shown in FIG. 25. Thosetwo labels individually overlie the respective button contacts mentionedabove.

As previously indicated, the differently-numbered pushbuttons ofkeyboard 110 also carry abbreviations relative to the days of the week.As specifically shown in FIG. 10, pushbuttons "1" through "7" aredenominated to indicate individually the respective days Sunday throughSaturday. Pushbutton "8" is assigned a designation "M-F" to indicateMonday through Friday, pushbutton "9" is designated with "S/S" toindicate Saturday and Sunday and pushbutton "0" contains the designator"A11". These different designations with respect to days of the week areintended to permit the user to enter a control program with respect toany specific day of the week, to apply a common program to anysuccession of five straight days such as Monday through Friday, to ordera different manner of operation for days off such as Saturday and Sundayor to select a manner of operation applicable to all days of the week.

Of course, the separation of Saturday and Sunday from Monday throughFriday as here shown by way of example is in accordance with what hasbeen the standard work week for a majority of the population. At thesame time, however, this assignment is entirely arbitrary and the usermay employ the sequence of numerals to reflect any choice as to thebeginning of a weekly cycle; that is, the pushbutton which bears numeralone could be used to designate a Wednesday, in which case the pushbuttonbearing numeral eight would apply to the days Thursday through Mondayand the pushbutton enumerated "9" would end up automatically applying toTuesday and Wednesday.

As present in FIGS. 9 and 14, the pushbuttons of keyboard 110 areexposed through openings in a bezel 220 mounted on a housing 222. Bezel220 surrounds the upper margin of a well 224 in which battery 152 is tobe located and which normally is covered by a plate 226 on the outersurface of which is printed a series of basic user instructions as shownbetter in FIG. 26. The content of those instructions will be appreciatedmore fully after consideration of the following description of useroperation. By observation of the small rectangles which correspond todifferent ones of the pushbuttons shown in FIG. 10, it will be seen thatthese instructions present a visual cross-reference. Of course, thelabeling as to each different instruction is self-evident. Nevertheless,the instructions set forth on panel 226 pertain only to the usual set ofinput entries required from the user. Instruction as to other possibleselected programming is to be included in an associated instructionmanual.

Bezel 220 also accommodates the light output from display device 200situated relative to appropriate indication of "TEMP", "DAY" and "TIME".This visual display will indicate those informational values as they arebeing programmed into the unit as well as indicate the same informationat any time that the REVIEW pushbutton is depressed. Thedifferently-numbered keys are used to relate to the days of the week asarbitrarily selected and assumed herein to begin with Sunday as well asto allow the input of desired temperature and time information.Overlying all of bezel 220, display device 200, keyboard 110 and plate226 is a transparent cover 228 hinged to swing to an open position, soas to allow access to the keyboard.

Depression of the START button always prepares the unit to receive newprogramming information and also functions to activate display device200 for a period of time, in the present case of about thirty secondsfrom the last depression of a key that causes microcomputer 150 to setup, enter or store data effectively received from or supplied to thedisplay, excepting error messages. The AM/PM button is used to select asbetween those respective portions of the time of day; as hereinembodied, each activation of the unit by use of the START button resultsin operation of the unit in the AM mode which will be indicated by theletter A at the right-most digit of the display. However, eachdepression thereafter of the AM/PM button will result in a switching asbetween AM and PM, and this button can be depressed to effect thatchange at any time. The CLEAR button is employed to erase informationtemporarily fed into the unit through the other pushbuttons butdetermined, by means of display device 200, to be incorrect; it also isused to erase any set of instructions when used in association with theREVIEW button as hereinafter described.

The STORE button instructs the unit to retain information "punched in"through use of the other buttons. That is, those other buttons are usedto enter information which is observed on display device 200 and, whenthat observation reveals correct entry, the store button then must bedepressed in order actually to load microcomputer 150 with thatinformation.

The REVIEW button activates display device 200 and allows the user todetermine both current environmental values and also to check the statusof instructions that previously have been placed into the unit. On thefirst depression of the REVIEW key, it indicates current temperature,day and time. When thereafter depressed repeatedly, it enables thesuccessive display on device 200 of the various sets of programmedinstructions. As will be discussed further below, cover 228 is so formedand mounted that, when lightly depressed inwardly, it activates theREVIEW pushbutton.

It should be noted that the user-programmable information desirablystored within the thermostat automatically is erased from its randomaccess memory at any time that supply power, by way of battery 152 andby way of input terminal 120, is removed. Whenever that has occurred andpower thereafter is restored, microcomputer 150, by reason of itspermanently stored program, will cause device 200 to flash the signal"HELP". That informs the user that the accessible memory is blank butready for again being programmed.

As an overview of user programming, START is depressed at the beginning;this activates the unit, including display device 200. Next, the timeclock is set. This is achieved by entering the temperature of zero-zerofor Celsius or zero-one for Fahrenheit followed by the day of the weekand the time of the day. Temperature control instructions are thenprogrammed into the unit, subject to always following a sequence oftemperature/day/time of day. A lighted bar appears at the appropriatelocation on display device 200 to make each sequence easier to follow byreminding the user what information is next to be entered. When thedisplay provided by device 200 indicates that the desired informationhas been supplied, the STORE button is depressed to cause that totalinstruction to be placed within the memory of the microcomputer. Thesame procedure is repeated for each different set of instructions withrespect to different days and times until all such information has beenstored.

As indicated on panel 226, also contemplated are the provisions foreither temporary override or what is termed vacation override. Use ofeither of those alternative operations enables the user to supercede theregular program while yet retaining that in the memory for subsequentuse as already programmed.

Also included is an error system which serves both to indicate a weakbattery condition and also to visually demonstrate when it has beenattempted to supply incorrect information. As specifically embodiedherein, four different error codes are included for visual display ondevice 200 of a heat-only model. When air conditioning also iscontrolled, there are two additional error codes. A mistake of entryresults in the flashing of an error code on device 200; under thatcondition, the unit will not accept the mistaken information. It issimply ignored, and proper information then is entered in place of thatwhich was ignored.

When an entry is made that is outside the acceptable design temperaturerange, (50°-89° F.) or (10°-29° C.) in the instant embodiment, thedisplay "Errl" will be visually produced. Also, the embodied unit isprogrammed so that, when first energized, it is automatically set toprovide indication in Celsius. Any attempt at that point to enter aFahrenheit temperature will result in the diplay of "Errl". To avoidthat error, the unit must first be programmed for Fahrenheit by usingthe zero-one code as above described. Again, should an improper entry beattempted, the unit will not accept it and the correct entry can thenimmediately be offered.

Should an "Err2" appear, that will mean that an improper day code wasemployed to originally set the time clock. This indicates that one ofpushbuttons "eight", "nine" or "zero" had been depressed instead of apushbutton assigned to a specific day. The display of "Err3" revealsthan an improper time was used in setting the clock. That will occur,for example, if the user attempts to enter a universal time such as thenumber "eighteen hundred". As embodied, the system contemplates use oftime information represented only in AM and PM modes. If desired,however, the ROM program could be changed to accommodate time on thebasis of a twenty-four hour format. In that case, of course, the AM/PMpushbutton no longer would be needed. When an instruction is enteredthat results in a temperature conflict as between heating and airconditioning, an "Err4" or "Err5" will appear. Besides giving thatmessage, the thermostat automatically resolves that conflict so thatboth heating and air conditioning cannot occur simultaneously.

Finally, and in connection with battery monitor 102, a display of thesignal "Err7" indicates that the battery is becoming weak. This warningwill be indicated upon depression of either a START or a REVIEWpushbutton for the first time. Upon quickly again depressing that key,the error code "Err7" will disappear, and the unit can again be normallyoperated until there is such additional degree of weakening of thebattery as to prevent operation in the battery-supplied mode, normalfunctioning always being available so long as the inputalternating-current is supplied to terminal 120.

It is significant to note that one purpose of including battery 152 isto preserve user-programmed information in the event of an externalpower failure during normal operation. Of course, the battery should bereplaced any time that the "Err7" signal appears. Battery 152 alsoserves to enable the unit to be disengaged from its mounting and, forexample, to be carried from room to room to check upon differenttemperature variations or to be placed on a table for convenience duringuser programming.

As specifically embodied in accordance with the foregoing description,it may be noted that there are twenty-three possible set points to anyinteger temperature from fifty degrees (50°) F. to eighty-nine degrees(89°) F. Each set point controls the temperature for a particular dayonly, a group of days or every day. Display device 200 automatically isdisabled after a preselected observation period, provided that thekeyboard has not been used during that interval in a manner to effect adata operation. In general, this exemplified system is designed tomaintain a temperature accuracy to within one degree Fahrenheit over theoperating range.

In a system which utilizes a pilot, such as a furnace fueled with gas oroil, it is possible to manipulate a conventional electro-mechanicalthermostat in a manner to literally blow out the pilot. This can occurif the gas valve is opened only for about one to two seconds and is thenclosed. That causes the flow of gas to be turned off at about the sametime that ignition occurs, and the resulting explosion or implosion mayextinguish the pilot. To avoid that possibility, and thus for thepurpose of safety, the values of capacitor C9 and resistor R20 areselected so that, together with inverters 210 and 211, there is a timedelay of about four and one-half (4.5) seconds after opening of the gasvalve before it can be closed.

As already indicated, the thermostat is contained primarily within ahousing 222. With reference to FIGS. 9-14, the overall assembly includesa mounting plate 240, a lower housing portion or base 242, a printedcircuit board 244, an upper housing portion or case 246, batterycompartment cover or plate 226 and transparent cover 228.

Mounting plate 240 is intended to be affixed to the wall of a room atthe location on the wall from which the wires that lead to the heatingand/or air conditioning systems emerge. Of course, any existingthermostat assembly is first removed. After feeding the wires through anopening in plate 240, the plate is secured to an electrical junctionbox, as provided in the wall and of typically appropriate size, ordirectly to the wall by means of suitable fasteners. In a manner to bedescribed further, the wires are connected to respective differentresilient contact members on plate 240. Also included on plate 240 arefastening parts that mate with other fastening parts on the bottom ofbase 242 in a manner to permit housing 222 thereafter to be mounted uponplate 240 by being simply slipped into place. At the same time, theaforementioned contact members are arranged in association with othercontacts in housing 222 so as automatically to complete electricalconnection to the thermostat. As desired at any time thereafter, housing222 may be slipped from its mounting upon plate 240 and carriedelsewhere. During that time of removal, the thermostat continues tooperate from its self-contained battery 152. The thermostat subsequentlymay be remounted upon plate 240 as easily as before.

FIG. 11 is a view of the side of mounting plate 240 that, wheninstalled, faces the wall. Also visible in FIG. 11 is the bottom of base242 as mounted in place upon plate 240. To be seen also are the heads oftwo of a total of four mounting screws 250 which project through base242 into engagement over a correspondingly aligned plurality of hollowposts 252 which depend downwardly from the top of case 246 forcompleting the assembly of housing 222 (FIGS. 17A and 18).

Mounting plate 240 is molded from an electrically-insulative plasticmaterial and shaped to include a matrix of reinforcing ribs 254 thatlend rigidity. A first pair of elongated holes 256 and 257 are locatedcentrally near respective opposing margins, and another space-opposedpair of elongated openings 258 and 259 are respectively located near theother pair of opposed side margins. The nominal distance between eachspace-opposed pair of openings 256-259 is the same as that between thethreaded mounting holes provided in a standard 2×4 inch electricaljunction box as often installed in the wall of a building for themounting of a thermostat. Thus, the two pairs of these holes permitmounting to such a box whether it is oriented horizontally orvertically. Moreover, the two of the holes in each space-opposed pairare elongated in respective directions at right angles to one another toaccommodate slight variations as among different junction boxes and alsoto allow the mounting of plate 240 in a level position even though thejunction box is a little tilted as installed in the wall. As indicatedabove, selected ones of holes 256-259 may, in the alternative, be usedfor the receipt of fasteners of some other kind used for the purpose ofsecuring plate 240 to the wall in a different manner. On the other sideof plate 240, as may be seen in FIG. 15, the reinforcing ribbing on thatsurface is formed as at 260, for example, to generally encircle each ofholes 256-259, and the surface is depressed within each suchencirclement so that a well is defined to accommodate the receipt of thehead of screw or other wall fastener and thereby not interfere with themounting of housing 222 and result in a thinner profile of the mountedthermostat.

Projecting outwardly from the lateral margins of plate 240, near itsbottom margin as mounted, are respective lugs 262 and 263. Alsoprojecting from those lateral margins, but near the top of plate 240 asinstalled, are respective ones of another pair of lugs 264 and 265. Asmay be seen in FIG. 15A, each of lugs 262 and 263 is shaped to define afinger 266 on which is formed a notch 268 from which the finger narrowsin the direction toward the open end of the lug. Lugs 264 and 265 havethe same shape except for the omission of notch 268.

Turning for a moment to FIG. 16 for a look at the bottom surface of base242, it will be observed to have a space-opposed pair of lateral marginareas 270 and 272 between which is recessed a panel 273 that constitutesmost of the bottom surface. Projecting toward one another from areas 270and 272 are a pair of respective ears 274 and 275 located in a positionbelow the middle of panel 273 as viewed in FIG. 16. Disposed upwardlytherefrom and projecting toward one another from margins 270 and 272 areanother pair of ears 276 and 277. With reference to FIG. 16A, it will beobserved that ear 275 is in the form of a finger 276 shaped to include anotch 278 from which the finger narrows toward the open end of the ear.Ear 276 is formed in the equivalent manner. Ears 276 and 277 are ofessentially the same shape as ear 275 except for the omission of notch278.

The different ones of lugs 262-265 are located in a pattern whichcorresponds with a pattern of respective ears 274-277. Lugs 262-265 maybe defined as slideways and ears 274-277 as guideways. To mountinghousing 222 upon mounting plate 240, therefore, it is only necessary toalign the various lugs and ears and slide them together into mutualinterrelationship. This is the same as if FIG. 16A were moved generallyto the left into FIG. 15A until finger 276 was fully beneath the fulllength of finger 266. Fingers 266 and and 276, and their correspondingequivalents, are slightly resilient as a result of which the differentnotches 268 and 270 become sufficiently interengaged to seat housing 222in proper position on plate 240, while yet permitting rather easydisengagement when desired. Note that FIG. 16A has been rolled overone-hundred-eighty degrees with respect to what normally would beindicated by the section line 16A--16A in FIG. 16.

Somewhat centrally disposed in mounting plate 240 is an opening 280spaced below another opening 282 slightly beneath which, as viewed inFIG. 11, is a smaller tab 283. During installation of mounting plate 240on the wall, the wiring preferably is led through opening 280 and thentucked under tab 283 (as viewed in FIG. 15) before being connected toswitch contacts mounted upon plate 240. If the wires are too short, theymay be led directly through opening 282.

Mounted on and projecting downwardly below the bottom margin of mountingplate 240 is installed is the free end 286 of a switch handle in theform of a lever 288 that has a pivot pin 290 captivated in a bearinghole 292, formed through plate 240, by a lip 294 which overlies a stub296 projecting radially outward from pin 290 (see both FIGS. 11 and 15).Stub 296 swings within an annular segment 298 opening outwardly from theupper side of bearing hole 292. Lip 294 only partially overlies segment298 so as to leave a small gap 300 through which stub 296 may beinserted into the segmental region beneath the lip during assembly.

Lever 288 has been removed in FIG. 15 but may be seen as mounted in FIG.14. Light finger pressure against its preferably knurled free end 286 issufficient to swing lever 288 about pin 290 between space opposed limits302 and 304 as defined by reinforcing ribs on the surface of plate 240visible in FIG. 15 and as seen in FIG. 14.

Also formed through mounting plate 240 are a first series of foursuccessively and laterally spaced like openings 306 and a fifth opening308 of the same shape spaced beyond that series and displaced slightlyin a downward direction as viewed in FIG. 11. Spaced respectively justbelow each of all of those openings are another series of four openings310 followed by a fifth opening 312 beneath opening 308. The spacebetween each upper and lower opening serves as a reinforcing rib 313 forthis region of plate 240 which otherwise might be excessively weakenedby the provision of so many openings in a limited area; rib 313 also hasanother purpose to be described below.

Viewable in FIG. 11 through all of the openings just described are thelegs of a plurality of resilient contacts 314, 315, 316, 317 and 318.Turning to FIG. 15, it will be observed that resilient spring contacts314 and 315 have been removed to permit a view of what lies beneath.Upstanding from the surface of plate 240 presented in FIG. 15 are aseries of vertically-oriented ribs 320 each successive pair of which isaligned with opposing sides of the different ones of openings 306, 308,310 and 312. Extending laterally across all of ribs 320 is a reinforcingrib 322. Toward the upper end of ribs 320 and respectively spanning thespaces therebetween are a series of webs 324 each of which includes anupwardly opening slot 326 which, as shown, diverges apart at its upperend portion. As viewed in FIG. 15, the bottom surfaces of rib 322 andwebs 324 are aligned at slightly above the level of the main surface 328of mounting plate 240 which extends between ribs 320. At the same time,the top surface of rib 313, as viewed in FIG. 15, is aligned at thatlevel.

Resilient spring contact 318 is shown in FIG. 19. It is formed as aspring-tempered strip of an electrically-conductive material such as aphosphor-bronze alloy and includes a leg 330 which merges into asmoothly-curved re-entrant bend 332. Beyond bend 332, the stripcontinues as a finger 334 bent away from leg 330 at its upper end, bentback toward leg 330 at an intermediate crease 336 and then once againbent slightly away from leg 330 at the beginning of its free end portion338. Starting at crease 336 and continuing through its free end portion338, finger 334 is necked down to a narrower width.

Near the lower end of leg 330, the strip is deformed over a smallcircular area to form a button 340 which faces finger portion 338.Intermediate the length of leg 330 is a cutout 342 shaped to leave anarrow projection 344 located centrally within cutout 342 and the freeend of which faces bend 332. Another cutout 346 is formed centrallyaround the circumference of bend 332 and in a manner to leave a stub 348that projects toward leg 330 with its free end spaced but a shortdistance therefrom when the contact is in its normal unflexed conditionas shown in FIG. 19. Also as a result of the formation of cutout 342, anear 350 is bent upwardly from leg 330 so as to project toward leg 334 adistance insufficient to interfere with the bending of finger 334 towardleg 330 an amount to move portion 338 against button 340.

For convenience, contacts 314-317 are identical to contact 318,although, as will become apparent, button 340 is superfluous on contacts315 and 316. The width of the strip from which the resilient contactsare formed is selected so that the width of leg 330 and bend 332 is onlyvery slightly less than the spacing between each pair or ribs 320. Thelatter, together with cross ribs 313 and 322 as well as web 324, definea channel within which the leg 330 of each contact is snugly receivedand seated. As each leg 330 is inserted into its channel, its free endpasses over cross rib 313, then under cross rib 322 and finally into aposition disposed in a very shallow channel 352 defined in surface 328of plate 340. Although thin, the finite thickness of leg 330 issufficient that the leg has to curve slightly over rib 313 which ends upbeing aligned near the bottom of cutout 342. As a result, the free endof projection 344 is deflected slightly toward finger 334, so as tobecome seated against the downwardly-facing end surface of web 324 asviewed in FIG. 11. Once mounted, therefore, each contact is constrainedto remain in place during connection of a wire to it and also duringmounting and dismounting of housing 222 from plate 240.

After installation of mounting plate 240 on the wall, the end portion ofeach wire is stripped of insulation for a short distance and the baredportion is inserted through cutout 346 in bend 332 and under stub 348until the end of the wire abuts ear 350. Even in the unflexed conditionof finger 334, the spacing between the free end of stub 348 and leg 330is sufficiently narrow that the bared wire end portion is gripped. Asfinger 344 subsequently is deflected toward leg 330 upon mounting ofhousing 322 to plate 340, that gripping pressure is further increased.

It will be seen in FIG. 14 that a pair of arms 354 and 356 projectgenerally outward from respective opposing sides of the upper end oflever 288. Affixed on the underside of those arms is an outwardly-facinggenerally C-shaped sheet of resilient conductive material the respectiveend portions of which define contact areas 358 and 360.

Area 358 is so shaped that it makes wiping connection with button 340 ofcontact 318 throughout the range of swing of lever 288. Moreover, area358 is also shaped and so disposed that, when lever 288 is swung towardits limit 302, area 358 comes into wiping connection over button 340 ofcontact 317. On the other hand, the swinging of lever 288 toward itsopposite limit 304 serves to bring area 360 into wiping contact overbutton 340 of contact 314. As already mentioned, the mounting of housing222 upon plate 340 results in flexural bending of fingers 334 toward thecorresponding legs 330. However, the free end portion 338 of the finger334 of each of contacts 314, 317 and 318 is shaped so at least thosefree end portions on contacts 314 and 317 are always clear of therespective ones of contact areas 358 and 360, so as not to interferewith movement of the latter into and out of connection with thecorresponding buttons.

Although it may be affixed in any suitable manner, the sheet which formscontact areas 358 and 360 is in this case staked onto mounting pins (notshown) on the underside of lever 288 as viewed in FIG. 14. Duringmovement of the lever, the ends of those pins ride within shallowchannels 362 and 364 (FIG. 15) defined in surface 328 of plate 240.Because legs 330 are seated into channels 352, contact areas 358 and 360ride over the very lower end of the corresponding legs 330 as theyapproach rounded buttons 340.

Referring back to FIG. 2, it may now be appreciated that lever 288serves as the switch for manually controlling the functions associatedwith the circulating fan or blower of an air conditioner. That is,contact 318 is terminal 140 and areas 358 and 360 constitute switchelement 142. Contact 317 corresponds to terminal 141, while contact 314corresponds to terminal 139.

Returning to FIG. 16, a generally-rectangular opening 366 is formedthrough panel 273 in a position to allow the central portion of thefingers 334 of each of contacts 314-317 to project therethrough whenhousing 222 is mounted on plate 240. At one side of opening 366, andrecessed into the surface of panel 273 as viewed in FIG. 16, is a shelf368. Shelf 368 is so positioned that, when housing 222 is mounted uponplate 240, contact 318 is aligned over the shelf. Because housing 222 isformed of a molded plastic which is an electrical insulator, this servesto isolate contact 318 from electrical components within housing 222,while at the same time ensuring that the finger 334 of contact 318 isdepressed so as to increase the gripping pressure of that contact uponits connected wire end. The upper and lower edge margins 370 and 372 ofopening 366 are beveled away from the opening so as to assist thecreases 336 of fingers 334 in gliding into and out of position ashousing 222 is mounted and dismounted from plate 240.

Formed through panel 273 at one corner of opening 366 is a circular hole374 of a diameter sufficient to permit the insertion of a screw driverfor a purpose later to be described. Centrally located in the upperportion of panel 273, as viewed in FIG. 16, is another somewhat largeand vertically elongated opening 376. To facilitate mounting of housing222 on plate 240, the thickness of plate 240 is tapered so as to becomethinner in the direction from lugs 262 and 263 toward lugs 264 and 265.That taper can be seen in FIG. 14. To allow an adequate recess for thehead of a screw inserted through hole 256, its surrounding rib 377projects above the level of the ribs 260 that encircle the othermounting holes. Opening 376 accommodates rib 377. Moreover, the sidewalls of opening 376 tend to guide rib 377 during mounting of housing222, so as to align ears 274-277 properly with lugs 262-265.

Also visible in FIG. 16 are a plurality of openings 378 through whichscrews 250 are inserted to enable engagement within the correspondinglypositioned hollow posts 252 formed in case 246. Each of openings 378 issurrounded by a boss which defines a seat so that the flat head of eachscrew 250 is out of the path of the bottom of housing 222 duringmounting and dismounting.

As may be observed in FIG. 14, the other side of each of openings 378 issurrounded by a boss 380 of an internal diameter sufficient to receiveand seat the very lower end of each of the corresponding ones of hollowposts 252 and thereby matingly align case 246 with base 242. Alsoprojecting upwardly from base 242 immediately on the inside, anddistributed around an upwardly facing rim 381 of the base, are aplurality of upwardly projecting guides 382 over which are fittedcorresponding portions of the lower margin of the skirt 284 of case 246.

FIGS. 17, 17A and 18 are views of case 246 as stripped of associatedparts shown in other views and some of which have already beenmentioned. For this discussion of case 246, it will be assumed that thecase is in an upright position as if the free margin of its skirt 284were placed against the wall. A control panel area 390 occupiesapproximately the upper two-thirds of case 246 and is tilted so that itsupper margin is spaced slightly to the rear of its lower margin.Continuing downwardly below control portion 390, as it slopes generallyto the rear before merging into skirt 284, is a lower panel 392.

Surrounding control portion 390 is an upstanding rim 394 which iscontinuous except for a gap 396 formed centrally in its upper leg.Immediately inside rim 394 throughout the extent of the latter, so asalso to include gap 396, is a shelf 398 upon which bezel 220 issupported as shown in FIGS. 10 and 14. Depressed further to the rearfrom shelf 398, and around both sides and across the top of batterycompartment 224, is a further shelf 400 upon which cover plate 226 is tobe mounted as shown in FIG. 10.

Battery compartment 224 is defined by a lower wall 402 (FIG. 17A), whichdepends rearwardly from near the upper margin of sloping panel 392, andan upper wall 404 that slopes rearwardly and downwardly from the uppermargin of shelf 400 and merges into a ledge 406 which projects towardwall 402. An opening 408 is located intermediate the width of wall 404and continues a short distance into ledge 406. Near the lower right-handcorner of ledge 406, as viewed in FIG. 17, is a small slit 410 throughwhich the leads to battery 152 are fed when the battery is installedwithin compartment 224.

Battery cover 226, with the decal 412 of FIG. 26 removed, is shown inFIG. 24. In FIG. 10, decal 412 is mounted in place upon the outersurface 414 of cover plate 226 that has rim 416 which surrounds thatsurface except for a gap 418 in the middle of the top margin. Decal 412is coated with a self-sticking adhesive on its undersurface so as tosecure itself to surface area 414 of cover 226 during assembly. Alongthe lower margin of cover 226 and projecting away therefrom is aninwardly-displaced lip 420. Projecting below surface 414 at the loweredge of an opening 421 therein is a tongue 422 having a catch 424. Toinstall cover 226, lip 420 is tucked behind shelf 398 at the lowermargin of battery compartment 224 and, as cover 226 is pushed intoplace, catch 424 slides down sloping wall 404 until it snaps intoopening 408 aligned therewith and latches against the upper margin ofthat opening. The engaging face of catch 424 is slightly canted so that,upon slipping a fingernail into gap 418 and under surface 414, cover 226is easily pulled open to permit access to the battery.

Spaced above battery compartment 226 is an opening 426 behind whichdisplay device 200 is to be mounted. Recessed below shelf 398 andsurrounding the top and both sides of opening 426 is a further sheft 428upon which a lens 430 (FIG. 10), shaped to fit snugly within the outlineof shelf 398, is mounted. Lens 430 is transparent but preferably of thesame color as the light emitted from display device 200 so as to improvecontrast of the displayed numbers and letters in the presence of ambientlight reflection from the lens.

The legend "TEMP DAY TIME", as shown in FIG. 10, is printed incontrasting color across the upper portion of lens 430 and is located soas to appear over the illuminated digits displayed. Display device 200is shown in FIG. 23A and will be observed to be of generally rectangularshape and comparatively thin. It features a row of lenses 431a behindthe operative ones of which are disposed light-emitting diodes of theseven-segment type as indicated in FIG. 5 (except for the color). Anarrow ledge 431b is formed on the lower margin along one side of therow of lenses, and a wider ledge 431c is provided along the oppositelower margin. A row of pin terminals 431d, corresponding to pinterminals 1-20 shown in FIG. 5, are disposed in ledge 431c.

Along the top and down both sides, as seen in FIG. 18, opening 426continues into a partial rim 432. Along the bottom of opening of 426,defined by a portion of shelf 398, is a ledge 434 just below which are apair of spaced posts 436. Disposed centrally along the upper margin ofopening 426, and projecting away from the lower surface of controlportion 390, is a tongue 438 having a catch 440 on its free end (FIG.17A). Spaced below and to the outside of posts 436 are a correspondingpair of cleats 442 which face catch 440 at the same level. Rib 432together with posts 436 and shelf 434 all form a seat for display device200. Lenses 431a, of course, face lens 430. Ledge 431c rests on posts436 and is confined under cleats 442. Ledge 431b rests on rim 432 and isengaged by catch 440.

Recessed below the level of shelf 398, and occupying a little more thanhalf of control panel 390, is a large flat area 460 on which keyboard110 of FIG. 25 is seated as shown in FIGS. 10 and 14. In contrast withFIGS. 10 and 14, however, the labels in FIG. 25 include both START HEATand START AIR legends in substitution for the single START label shownin the earlier figures. Formed through panel 390 along the bottom ofarea 460 is a narrow slit 462 through which a flat flexible package orcable 464, within which are a plurality of conductive leads as indicatedat 466, is inserted and fed as keyboard 110 is moved into position onarea 460.

A wide variety of keyboard assemblies are available in the marketplace,and the configuration of case 246 could be adapted to accommodate anumber of them. The particular keyboard assembly embodied herein andillustrated in FIG. 25 is a very thin sandwich of several flexiblelayers of insulating material. From the perspective of viewing FIG. 25,there is an underlying layer on the bottom surface of which is aself-sticking coat of adhesive covered with a peel-off plastic-coatedprotective paper sheet which, during assembly, is peeled off to permitthe keyboard assembly to be adhesively secured to area 460. An array ofconductive contact pads, distributed in a pattern corresponding to thelayout of "keys" or "buttons" depicted in FIG. 25, is printed upon theupper surface of that first flexible layer along with severalinterconnecting leads as defined in FIG. 5 and which continue withincable 464.

Lying on top of that first flexible layer is a sheet of insulatingmaterial through which is defined an array of openings that expose eachof the contact pads printed upon the upper surface of the first layerbut cover the wiring also printed on that first layer. Such openings areknown in the art as "cages". Overlying that layer of cages is a thirdflexible sheet of insulating material on the lower surface of which,facing the cage sheet, is printed another array of conductive contactpads individually disposed so as to be aligned over respective differentones of the contact pads printed on the first layer and, thus, alsoaligned with the cage openings. Also included on the undersurface ofthis third flexible layer is the necessary additional wiring, again asdefined in FIG. 5, which similarly is extended down cable 464. Asdiscussed previously in connection with FIG. 5, the contact pad printedon this third layer and underlying the START position in FIGS. 10 and 14is separated into a pair of slightly spaced segments each having anindividual printed connection and which individually underlie therespective START HEAT and START AIR positions as shown in FIG. 25.

Printed on the upper surface of the flexible third layer is a grid inthe form of a succession of laterally spaced narrow conductive linesthat are all electrically connected together and to a conductor withincable 464. It is that conductive grid which serves as electrostaticshield 192 previously discussed in connection with FIG. 5. Finally, adecal 468, carrying the printing indicated in FIG. 25 (or as indicatedin FIG. 10 for a heat-only model), is adhesively fixed on top of thethird layer and over the conductive grid. The intermediate cage-forminglayer is sufficiently thin that only light finger pressure applied onany key or buttom area is enough to move the uppermost one of theunderlying pads through the cage opening and into contact with thebottom contact pad, so as to complete a connection and thus close the"pushbutton".

After keyboard assembly 110 has been affixed to surface 460, bezel 220is cemented or otherwise secured so as to overlie the keyboard anddefine the pushbutton openings as well as to frame both batterycompartment 224 and opening 426, bezel 220 generally lying on top ofshelf 428. The opening over battery compartment 224 is sufficientlylarge to accept battery cover 226 while the bezel strip at the bottom ofopening 426 projects slightly over that opening in order further toconfine lens 430 in place. Similarly, the surrounding portions of thebezel serve to additionally secure the edge margins of keyboard assembly110. For the specific keyboard shown in FIG. 25, it is preferred thatbezel 220 include a leg disposed between the pair of "start" buttons.

Formed around the lower margin of skirt 284 of case 246 is a downwardlydepending lip 470 havng a downwardly-facing end surface aligned with theupperwardly-facing surface of rim 381 around the margin of base 242.When case 246 is mated to base 242 and the lower ends of posts 252 areseated within wells 380, lip 470 closes the space between case 246 andbase 242 except at a gap 472 in lip 470, near the lower left hand cornerof case 246 as viewed in FIG. 18, and a plurality of gaps 474 formed inlip 470 and distributed along the upper margin of case 246. When base242 and case 246 are joined together, those gaps define openings intothe interior of housing 222. As seen in FIG. 12, gap 472 is disposed atthe bottom of the housing when housing 222 is mounted on plate 240 so asto be vertically oriented. The purpose of these various openings definedby gaps 472 and 474 will be set forth below.

Again viewing the bottom of case 246 as shown in FIG. 18, a web 475 willbe seen to extend all of the way between skirt 284 and an end wall 476of battery compartment 224, the battery compartment being completed bythe formation of an opposing end wall 478. Web 475 is located just aboveslit 462 along the lower margin of area 460 and thus serves to rigidifythe latter. Connected between skirt 284 and the pair of posts 252 alongthe lower margin of case 246 are webs 480 which are formed integrallywith the underside of sloping panel portion 292. Each of webs 480defines a flat 482 disposed in alignment with about the middle of theopening defined by gap 472. The outer ends of posts 252 project beyondflats 482 by a distance slightly greater than the thickness of printedcircuit board 244.

Post 252 toward the upper left-hand corner of FIG. 18 is supported fromthe underside of area 460 by upstanding generally-triangular-shaped andspace-opposed webs 484 and 486 each of which is slightly truncated inorder to define respective flats 488 and 490 which are at the same levelas flats 482. Moreover, the undersurface of ledge 406 adjacent to theremaining post 252 is also at the level of the different flats justdiscussed. The uppermost ones of these other posts 252 project beyondthat level to the same extent as the lower posts 252. Included at theupper left-hand corner of the battery compartment as seen from thebottom in FIG. 18, and in alignment with opening 374 in base 242, is anadditional hollow post 490 the outer end of which is also disposed atthe level of the different flats and the undersurface of ledge 406.

Circuit board 244 is dimensioned to be received within lip 470 andincludes four openings 492 distributed in a pattern corresponding to thepattern of layout of posts 252 and each of a diameter to fit with onlyslight tolerance over the protruding ends of the respective posts. Thus,upon assembly, circuit board 242 rests upon all of the different flats,the top of additional post 490 and the facing surface of ledge 406.Circuit board 244 has a thickness such that the outer end portions ofposts 252 project through board 244 a distance just sufficient to enterinto the wells defined within bosses 380 on panel 273 of base 242.Therefore, when screws 250 are inserted from the bottom of base 242 andtightened into the bores of posts 252, circuit board 244 is clampedtightly into a fixed position within the housing. Also formed throughcircuit board 244 is an aperture 494 which, when the circuit board ismounted in place over posts 252, is aligned with the bore of post 490.

Board 244 is of conventional construction, being composed of asemi-rigid insulative substrate through which are formed a largeplurality of small pin apertures each sized to receive the conventionalwires from discrete electronic components and terminal pins whichproject outwardly from integrated circuits and the like. The undersidecarries a printed circuit defined in accordance with FIGS. 2-5. Ittypically may be formed by coating the undersurface with a thin layer ofcopper and then, using a conventional photoresist or similar maskingtechnique, etching away selected areas of the copper so as to leave onlythe desired conductive paths that interconnect the various differentones of the pin apertures as needed to complete the circuitry and alsoto form a small conductive soldering ring surrounding each pin orwire-receiving aperture. At the same time, four much larger conductivepad areas, each about the size of a numbered pushbutton area of keyboardassembly 110 which is drawn to scale, are formed and disposed inpositions to be aligned respectively with the fingers 334 of contacts314-317 when those fingers project through opening 366 in panel 273 uponmounting of housing 222 to mounting plate 240. That is, the crease 336of each finger 334 constitutes an electrical contact which is wipedagainst a respective one of the large conductive pads, printed on theundersurface of circuit board 244, as housing 222 is mounted on plate240. Accordingly, the wires secured to each of contacts 314-317 areconnected by creases 336 of fingers 334 into the circuitry defined onboard 244 through the mere act of mounting housing 222 upon plate 240.

A pair of electrically separate contact ring segments also are formed soas together almost to complete encirclement of opening 494. Withreference to FIG. 2, those two rings constitute terminals 120 and 141.When a small screw is inserted through opening 374 in base 242 andthreaded into the bore of post 490 through aperture 494, the head of thescrew conductively bridges those two segments when the screw istightened. Consequently, the screw head serves the function of jumper143. Preferably, all of the plated and etched undersurface is coatedwith an insulating material except for the immediate sites of each ofthe different conductive pads and rings.

Subject to a fiew constraints, the layout of the various differentcomponents on the upper surface of board 244 is primarily determined byspace considerations and the necessary distribution of the printedwiring pattern on the underside of the board. One such constraintpreviously mentioned was the desirability of locating capacitor C13physically close to the Vcc terminal of microcomputer 150. Another is toprovide a series of connection apertures in a position convenient forthe coupling of cable 464 (see FIG. 22A). Of similar consideration wouldbe the provision of another series of connecting apertures directlybeneath display device 200. Additionally, thermistor RT1 of temperaturesensor 108 (FIG. 3) is located immediately inside the opening defined bygap 472.

During operation, the various electrical components within housing 222dissipate a small quantity of heat. The dissipation of that heat createsa chimney effect between the lower opening defined by gap 472 and theupper openings defined by gaps 474 as well as other more upward openingsthrough which there is a degree of leakage. This chimney effect createsa continual flow of room air into the lower opening at gap 472 and outof the more upwardly disposed openings. Being located just inside theopening defined by gap 472, thermistor RT1, therefore, is able to obtainan accurate reading of the actual temperature of the room air withoutdistortion by, but taking advantage of, the heat dissipated by the otherelectrical components.

For completing a connection between the conductors within cable 464 andthe circuitry printed on board 244, a plurality of connectors 496 areemployed. Each connector, as shown in FIGS. 22A and 22B, is necked downat its lowered end to define a pin 498 which is received within apin-connecting aperture in board 244. Projecting upwardly from the bodyof connector 496 is a central tong 500 on either side of which is a bentresilient finger 502. At the lower end of cable 464, the covering overthe printed conductors 466 is cut away to expose the conductor ends. Inthis case, the upper and lower surfaces of cable 464 are simplycontinuations of the first and third flexible layers mentioned above inconnection with the discussion of keyboard 110. Accordingly, some ofconductors 466 are affixed to the upper surface of the first layer,while the others are affixed to the lower surface of the third layer.

With a plurality of connectors 496 disposed in a row as indicated inFIG. 14, it is only necessary to insert the lower end portion of cable464 between the rows of opposing fingers and in a manner such that eachexposed contact end is slipped between the tong 500 and gripping fingers502 of the appropriate one of connectors 496. In this case, of course,the row of connectors 496 on board 244 is so disposed as to be aligneddirectly ahead of cable 464 as it emerges from slit 462.

A different form of connector 506, shown in FIG. 23B, is employed toconnect display device 200 into the circuitry. The central body portionof connector 506 is necked down at its lower end 508 to define a pinagain receivable in a selected pin aperture formed in board 244. At itsupper end, connector 506 has a projecting thumb 510 alongside a longerfinger 512 slightly bent at its outer end portion toward thumb 510.During assembly, thumb 510 and finger 512 are inserted through anappropriate one of pin terminals 431d in ledge 431c of device 200 whichis disposed directly above the row 514 of connectors 506 disposed on theupper surface of board 244. Thumb 510 and finger 512 press against andmake contact with the conductively plated interior of the correspondingpin terminal opening.

In an alternative manner of securing device 200, a mounting rack 515 asshown in FIG. 23C is used. To this end, posts 436, tongue 438 and cleats442 are omitted, and rim 432 has another portion running between thelocations of posts 436 as they actually are shown. Disposed just behindrow 514 of connectors 506 as viewed in FIG. 14 are a pair of holes whichseat the lower ends of legs 516 on rack 515. An array of shorter legs517 rest on top of board 244 in front of row 514. A row of openings 518in rack 515 are aligned with respective connectors 506, so that thumbs510 and fingers 512 project about half way therethrough. Device 200 maybe mounted on rack 515 before case 246 is placed on base 242, allowingtesting before final assembly of the housing. Upon that assembly, ledges431b and 431c rest on rim 432 as extended.

Transparent cover 228 is formed of a material such as polycarbonate. Itincludes a main flat panel 520 around the entire margin of which is adownwardly depending skirt 522 which, when cover 228 is in a closedposition, is spaced alongside and outwardly from rim 394 with the lowermargin of skirt 522 normally being slightly spaced above a ledge 524which entirely surrounds rim 394 except at gap 396 (FIG. 17).

On the undersurface of panel 520, equally spaced about the center of therear margin of the panel and merged into the inner surface of thatportion of skirt 522, are a pair of spaced blocks 526 and 528. Eachblock includes a lateral circular opening 530 which communicates with apassage 532 of a width slightly smaller than the diameter of opening530. Depending downwardly from the inner surface and near the rearmargin of panel 520, and spanning the distance between blocks 526 and528, is a rib 534 that slants up toward the rear.

With reference to FIGS. 17 and 17A, depending downwardly beneath and atthe edges of gap 396 are a pair of respective webs 536 and 538. Spaced ashort distance from gap 396 beyond each of webs 536 and 538 are anotherlike pair of corresponding webs 540 and 542. Each of these webs includesa downwardly-opening generally-circular recess 544 open on its lowerside to communicate with a slightly narrower passage 546.

Each of openings 530 in blocks 526 of transparent panel 228 constitute ahinge. Similarly, each of recesses 544 in webs 536 and 540 constituteanother hinge, while those same recesses 544 in webs 538 and 542constitute a still further hinge. Cooperating with all of those hingesis a hinge bar 550. As shown in FIG. 20, hinge bar 550 is of somewhatC-shaped cross section. Its lower leg 552 is generally straight but isbent slight outwardly from a generally V-shaped bight portion 554. Itsupper leg 556 curves smoothly away from portion 554 to present a convexouter surface. An ear 557 projects outwardly from each end of bightportion 554.

Projecting laterally outward from one end of leg 552 is a hinge pin 558.Similarly projecting outwardly from the other side of leg 552 is anotherhinge pin 560. The outer end portion of leg 556 is necked down at 562.Projecting laterally outward from the end of that necked down portion ofleg 556 is a pin 564 on one side and a pin 566 on the other.

Hinge bar 550 swings within the opening 568 provided by gap 396. Pin 558is captivated within recesses 544 of webs 536 and 540, while pin 560 iscaptivated within recesses 544 of webs 538 and 542. Bight portion 554faces generally in a downward direction and the outer curved surface ofleg 556 rides alongside the bottom margin 572 of opening 568 as hingebar 550 swings about hinges 558 and 560. Bottom margin 572 is beveledinwardly in a direction downwardly from opening 568 as shown in FIG. 18.

Pin 564 is captivated within opening 530 of block 526, while pin 566 iscaptivated within the identical opening within block 528. Thus,transparent cover 228 may, to a limited extent, be swung about pins 564and 566. Centrally disposed between approximately the rear sides of pins564 and 566, as viewed in FIG. 20, and projecting outwardly from theoutside surface of leg 556, is a lug 570.

With cover 228 in the closed position, the cover is hinged around pins564 and 556 so as to be swung over leg 556 to a position such that lug566 projects into the recess formed by the outside of rib 534. At thesame time, hinge bar 550 has been swung downwardly within opening 568 sothat lower leg 552 is approximately parallel with control panel 390. Ascover 228 is first swung away from its closed position, interferencebetween lug 570 and rib 534 retards rotation of pins 564 and 566 as aresult of which hinge bar 550 first swings upwardly about pins 558 and560 until the ears 557 on the sides of bight 554 engage the lower sideedges of opening 568. Thereafter, further opening of cover 228 causes itto complete its limited movement of swing, which may already have beenstarted, about pins 564 and 566. That limit is reached when skirt 522touches the inside of leg 566. On still further opening of cover 228,ears 557 cam inside the side walls of opening 568 as hinge bar 550 isswung on around pins 558 and 560 until a limit is reached when theinside of leg 552 abuts the inner surface of skirt 284 of upper housing242.

When cover 228 has been moved to the fully opened position, thedimensions and the backward slope of control panel area 390 such that ittilts backward a slight amount, so as to remain in the open positionwith respect to swinging about pins 564 and 566. At the same time, thefrictional engagement of ears 557 with the side surfaces of opening 568retains hinge bar 550 in its open position. The double articulationprovided by the combination of the two different sets of hinges enablescover 228 to be both fully closable and openable a fullone-hundred-and-eighty degrees to a position in which it is entirely outof the way of operation of keyboard 110.

Also projecting downwardly from the inner surface of panel 520 is a boss574. The latter has approximately the shape of and, when cover 228 isclosed, is oriented with and aligned directly over the REVIEWpushbutton. Moreover, the lower end 576 of boss 574 is, with the covernominally closed, spaced only slightly above or just at the surface ofthat REVIEW pushbutton. The material of cover 228 is slightly flexibleand the slight normal spacing of the bottom of skirt 522 from ledge 524allows pressure anywhere upon the exposed face of panel 520 to causedepression of the REVIEW button by boss 574 and thereby immediatelyprovides a readout of temperature, time and day from device 200 withoutopening the cover. Repeated application of pressure upon cover 228, ofcourse, would enable a user to conduct additional review as previouslydescribed, such as determining what is to happen next. At the same time,this operation cannot cause an alteration of any program step that hasbeen stored. In addition, cover 228 serves as a dust protector and alsoas a deterrent against undesired pushbutton manipulation by PG,70others. Being transparent although it may be tinted, and also having thereview actuation feature, there seldom is any need to open cover 228unless a battery warning is observed or it is desired to make a changein the programmed operation.

It will be observed that a wide variety of different features have beendisclosed. Without limitation or ordering as to importance, it may benoted that a common temperature sensor is employed for control of eitherheating or air conditioning. Moreover, that sensor is disposed in arestricted air flow path by an arrangement which tends to preventmisleading readings that otherwise might result from transient aircurrents. The overall layout creates a chimney effect which insures thatroom air constantly is drawn through the unit in order to provide anaccurate response.

The particular hinge arrangement, including hinge bar 550, permits cover228 to be swung more than one-hundred-eighty degrees while yet allowingcomplete closure. This hinge arrangement achieves what may be termed adual-detenting so as to insure that it opens and closes in propersequence. Resilient contacts 314-317 exhibit a double action thatpermits contact both to the printed wiring and to the incoming supplyand command leads. Those contacts also permit the unit readily to beremoved from the wall simply by taking advantage of the different earsand lugs provided as between the housing and the mounting plate.

Involving both battery and external alternating-current power supply, arather sophisticated switching arrangement is provided in order tochange between those two different supplies. Yet, the unit is arrangedto run normally from the external alternating-current supply. Battery152 not only provides a backup to the main power supply system but alsoenables retention of the stored user programs should there be a powerfailure or should the user desire to displace the controller to anotherlocation for reasons already indicated. In addition, the unit warns theuser when it becomes time to replace battery 152.

Electrostatic screen 192 disposed over keyboard 110 serves to protectagainst damage to the sensitive microcomputer. In addition, there arevarious filters and optical couplers to provide suppression oftransients and other spurious signals which otherwise might beintroduced by reason of signals appearing on the incomingalternating-current power supply or from other sources. Additionalfiltering is included in order to protect against radio-frequencyinterference. An included time delay prevents control operation in anundesired manner which otherwise might even cause a pilot light in anassociated heating or cooling unit to be extinguished.

Even though involving only what basically is a simpleresistance-capacitance circuit, the temperature sensor is caused to besufficiently linear as to be accurate within one degree Fahrenheit overthe rather broad functional range. The unit gives notice that thecontrol is calling for heat, serving to assure the user that heat isbeing supplied by a "silent" arrangement such as a heating system whichuses hot water, steam or radiant supply. Even in the case of a forcedair system, the indicator serves to inform the user that externaloperation has been commanded prior to the expiration of the time delaythat often occurs between initial energization and the operation ofblowers or the like.

The software incorporated is of special advantage. For example, theorder of data entry established makes it possible to "write a sentence"instead of having to make constant use of an "enter" key. The day codesassigned to the numbered entry keys allows substantial flexibilitywithin the user's normal work week. On the other hand, the user who hasa rather non-typical schedule of events easily can employ the individualday codes to arrange a program in accordance with his own uniqueschedule.

Adding to flexibility is the feature of temporary override that affectsonly one previously-programmed instruction without, nevertheless,removing that previous instruction. Similarly, the vacation overrideenables a different program to be followed during a longer period oftime and again without disturbing the normal program.

Having both Fahrenheit and Celsius scales, the thermostat contemplates apossible switchover in common usage from one to the other. Moreover, thethermostat features a manner of conversion which effects a change of anentire sequential program as between Fahrenheit and Celsius, while atthe same time changing the corresponding visual display.

The particular unit as embodied is capable of accepting up totwenty-three set points. Considering the various different day codeoptions, this means that the user can establish in excess of one-hundreddifferent temperature set points within any given week.

In the overall, therefore, the user is enabled to program theestablishment of his own comfort level which he desires over a widevariety of different periods throughout an entire week. At the sametime, the user can achieve energy conservation by focusing ratherspecifically upon fairly narrow time periods during which demanddesirably should be lessened in order to effect such conservation.Moreover, the thermostat affords simultaneous control of both heatingand air conditioning with requiring that the user act to switch betweenthe two systems. Thus, he is further able to program the establishmentof his own complete "comfort zones".

Certain aspects of the present invention are described and claimed inconcurrently-filed co-pending applications Ser. No. 069,870 of James B.Waite, Myron Yoknis and Robert M. Neel under the title "ProgrammableThermostat" and Ser. No. 069,978 of James B. Waite and Myron Yoknisunder the title "Thermostat Assembly", both being assigned to the sameassignee as the present application.

While a particular embodiment of the invention has been shown anddescribed, and numerous modifications and alternatives have beensuggested, it will be obvious to those skilled in the art that otherchanges and modifications may be made without departing from theinvention in its broader aspects. Therefore, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

I claim:
 1. A thermostat assembly comprising:a housing assembly; switching means mounted on said assembly for selective operation by the user; an indicator mounted on said assembly for signaling to the user; a circuit unit mounted within said assembly and interconnected to receive signals from said switching means and to deliver signals to said indicator; a temperature sensor mounted within said assembly and responsive to ambient air temperature to deliver a temperature-representative signal to said circuit unit; connecting means for coupling said circuit unit to an external device to be controlled in response to operation of said switching means and governed in response to said temperature-representative signal; a mounting plate affixable to a wall surface and having means for removably securing said assembly latchably thereto in a fixed position fully juxtaposed therewith; a plurality of electrical contact pads mounted in one to face the other of said assembly and said plate; a plurality of resilient electrical contact fingers mounted in the other of said assembly and said plate and aligned to mate and slide into contacting engagement with said pads as said assembly and said plate are secured together; means for coupling one of said pads and said fingers to said external device; and means for coupling the other of said pads and said fingers to said circuit unit.
 2. A thermostat assembly as defined in claim 1 in which each of said contact fingers is a portion of a strip another integral portion of which defines a bend continuing re-entrantly into a leg generally disposed alongside and co-extensive width the finger.
 3. A thermostat assembly as defined in claim 2 in which each of said fingers is bent intermediate its length to define a crease facing away from said leg and engageable with a corresponding one of said pads.
 4. A thermostat assembly as defined in claim 1 in which said assembly includes a panel in which is defined an opening through said which said contact fingers extend.
 5. A thermostat assembly as defined in claim 4 in which said circuit unit includes a substrate disposed inside said opening and on which said contact pads are disposed, said contact fingers being carried by said plate.
 6. A thermostat assembly comprising:a housing assembly; switching means mounted on said assembly for selective operation by the user; an indicator mounted on said assembly for signaling to the user; a circuit unit mounted within said assembly and interconnected to receive signals from said switching means and to deliver signals to said indicator; a temperature sensor mounted within said assembly and responsive to ambient air temperature to deliver a temperature-representative signal to said circuit unit; connecting means for coupling said circuit unit to an external device to be controlled in response to operation of said switching means and governed in response to said temperature-representative signal; a mounting plate affixable to a wall surface and having means for removably securing said assembly thereto; a plurality of electrical contact pads mounted to one of said assembly and said plate; a plurality of resilient electrical contact fingers mounted in the other of said assembly and said plate and aligned to mate with said pads when said assembly and said plate are secured together; means for coupling one of said pads and said fingers to said external device; means for coupling the other of said pads and said fingers to said circuit unit; each of said contact fingers being a portion of a strip another integral portion of which defines a bend continuing re-entrantly along a leg disposed generally alongside the finger; each of said fingers being bent intermediate its length to define a crease facing away from said leg and engageable with a corresponding one of said pads; each of said fingers also being bent intermediate said crease and its free end to define an end portion normally diverging away from said leg but matable against the free end portion of said leg upon flexure of the finger toward the leg.
 7. A thermostat assembly as defined in claim 6 in which a contact button is formed in said free end portion of said leg facing said end portion of said finger.
 8. A thermostat assembly comprising:a housing assembly; switching means mounted on said assembly for selective operation by the user; an indicator mounted on said assembly for signaling to the user; a circuit unit mounted within said assembly and interconnected to receive signals from said switching means and to deliver signals to said indicator; a temperature sensor mounted within said assembly and responsive to ambient air temperature to deliver a temperature-representative signal to said circuit unit; connecting means for coupling said circuit unit to an external device to be controlled in response to operation of said switching means and governed in response to said temperature-representative signal; a mounting plate affixable to a wall surface and having means for removably securing said assembly thereto; a plurality of electrical contact pads mounted in one of said assembly and said plate; a plurality of resilient electrical contact fingers mounted in the other of said assembly and said plate and aligned to mate with said pads when said assembly and said plate are secured together; means for coupling one of said pads and said fingers to said external device; means for coupling the other of said pads and said fingers to said circuit unit; each of said contact fingers being a portion of a strip another integral portion of which defines a bend continuing re-entrantly into a leg disposed generally alongside the finger; and means defined in said bend for gripping a wire end inserted through said strip at said bend.
 9. A thermostat assembly comprising:a housing assembly; switching means mounted on said assembly for selective operation by the user; an indicator mounted on said assembly for signaling to the user; a circuit unit mounted within said assembly and interconnected to receive signals from said switching means and to deliver signals to said indicator; a temperature sensor mounted within said assembly and responsive to ambient air temperature to deliver a temperature-representative signal to said circuit unit; connecting means for coupling said circuit unit to an external device to be controlled in response to operation of said switching means and governed in response to said temperature-representative signal; a mounting plate affixable to a wall surface and having means for removably securing said assembly thereto; a plurality of electrical contact pads mounted in one of said assembly and said plate; a plurality of resilient electrical contact fingers mounted in the other of said assembly and said plate and aligned to mate with said pads when said assembly and said plate are secured together; means for coupling one of said pads and said fingers to said external device; means for coupling the other of said pads and said fingers to said circuit unit; each of said contact fingers being a portion of a strip another integral portion of which defines a bend continuing re-entrantly into a leg disposed generally alongside the finger; means on said plate defining a plurality of channels in which respective different ones of the legs of said fingers are seated; and each of said channels including means defining an abutment, each of said legs including means defining a flexible projection, and each of said channels also including means for flexing said projection into locking engagement with said abutment upon seating of the leg in the channel.
 10. A thermostat assembly comprising:a housing assembly; switching means mounted on said assembly for selective operation by the user; an indicator mounted on said assembly for signaling to the user; a circuit unit mounted within said assembly and interconnected to receive signals from said switching means and to deliver signals to said indicator; a temperature sensor mounted within said assembly and responsive to ambient air temperature to deliver a temperature-representative signal to said circuit unit; connecting means for coupling said circuit unit to an external device to be controlled in response to operation of said switching means and governed in response to said temperature-representative signal; a mounting plate affixable to a wall surface and having means for removably securing said assembly thereto; a plurality of electrical contact pads mounted in one of said assembly and said plate; a plurality of resilient electrical contact fingers mounted in the other of said assembly and said plate and aligned to mate with said pads when said assembly and said plate are secured together; means for coupling one of said pads and said fingers to said external device; means for coupling the other of said pads and said fingers to said circuit unit; each of said contact fingers being a portion of a strip another integral portion of which defines a bend continuing re-entrantly into a leg disposed generally alongside the fingers; means for mounting said fingers on said plates a switch handle movably mounted on said plate; and electrical contact areas affixed to said handle and selectively engageable with different ones of said legs upon movement of said handle between different positions thereof.
 11. A thermostat assembly comprising:a housing assembly; switching means mounted on said assembly for selective operation by the user; an indicator mounted on said assembly for signaling to the user; a circuit unit mounted within said assembly and interconnected to receive signals from said switching means and to deliver signals to said indicator; a temperature sensor mounted within said assembly and responsive to ambient air temperature to deliver a temperature-representative signal to said circuit unit; connecting means for coupling said circuit unit to an external device to be controlled in response to operation of said switching means and governed in response to said temperature-representative signal; a mounting plate affixable in parallel to a surface and that has means defining slideways generally parallel to said plate; and a wall forming a part of said housing assembly and having means defining guideways generally parallel to said wall and disposed in alignment with said slideway, when said wall is parallel to said plate, to enable removable mating therebetween and consequent mounting of said assembly latchingly to said plate. 